Portable cathode-ray oscilloscope



I April 27 1948. w, CHALBERG 2,440,538

PORTABLE CATHODE RAY OSCILLOSCOPE Filed April 26, 1946 3 Sheets-Sheet 1wm I a:

unngunnu n'nnun Inverwtorw Harry WA Chalber g,

i o KL I b April 27, 1948.

H. W. A. CHALBERG PORTABLE CATHODE RAY OSCILLOSCOPE Filed April 26, 19463 Sheets-Sheet 2 Inventor:

Harry W A. Chal berg,

' His Attorney.

April 27, 1948. w CHALBERG 2,440,538

PORTABLE CATHODE RAY OSCILLOSCOPE I Filed April 26, 1946 3 Sheets-Sheet3 Inyerwtor: Harry W A. Chalberg,

b Hi5 Attorney voltage dividers Patented Apr. 27, 1948 PORTABLECATHODE-RAY OSCILLOSQOPE Harry W. A. Chalberg, Berne, General ElectricCompany,

New York Application April 26, 1946, Serial No. 665,304

2 Claims. 1

My invention relates to cathode-ray oscilloscopes and one object is toprovide a portable oscilloscope that may be housed in a portablecontainer comprising an ordinary luggage or suitcase. Other objectsrelate to certain improvements in the control circuitsemployed to obtainsimplicity, ease and accuracy of calibration and operation, variation,without sacrificing reliability for general industrial use. Certainaspects of my invention disclosed but not claimed herein are claimed indivisional applications Ser. No. 8804, filed February 1'7, 1948; andSer. No. 8805, filed February 1'7, 1948.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claims appended hereto. For abetter understanding of my invention, reference is made in the followingdescription to the accompanying drawings in which Fig. 1 Ba wiring dia-N. Y., assignor to; a corporation of and independence of line voltagegram of the oscilloscope apparatus; Fig. 2 is a front view of theoscilloscope as assembled in its carrying case with the cover of thecase removed preparatory to using the oscilloscope; Fig. 3 shows a rearview of the oscilloscope chassis as removed from its carrying case; Fig.4 shows connections of a plug-in attenuator and Fig. 5 is a modifiedimage distortion control.

In Fig. 1 of the drawing there is represented the wiring diagram of theoscilloscope. The oscilloscope cathode-ray tube l with its focus control2, sensitivity control 3, and astigmatism control 4, is represented inthe upper right of Fig. 1. The power supply pack for the oscilloscopeand its circuits is conventional and is represented in the lower rightof Fig. 1, and. consists of a transformer 5 having the necessarysecondary windings for supplying the filament heater circuits designated:1; and y, the full wave rectifier tube '6, the half wave rectifier tube1 for supplying the high voltage cathode circuit of the oscilloscope, 8and 9, and voltage regulator tube l0. Typical D.-C. voltages employedare indicated at important points in the power supply. The verticalamplifier for the oscilloscope is generally designated at II, thehorizontal amplifier at 12, and the sweep voltage generator at I3. At Mis a switch which is used to connect the vertical amplifier input signalterminals l5 and H5 or calibrating voltages from voltage divider 9 tothe input of the vertical amplifier II. The vertical amplifier input ismade control variable resistance circuits having high and low variableresistances l1 and I8 and high and low fixed resistances l9 and 20.

through one of the gain The particular gain control resistance circuitused is selected by means of switch 2|. Four different ranges ofresistance control are provided for and in each case one or the other ofthe variable controls I! or; I8 is included. ;It ispoted that suchvariable resistance gaincontrol is available both when the input isconnected to the signal terminals l5 and War to; the calibratingvoltages from voltage dividerS. When A.C. signal voltages are beinginvestigated, the input terminals 15 and 22 are used. Terminal 22 is agrounder common terminal 1 and is, connected to the metal chassis of theapparatus; For'the A.-C. signal connection the condenser 23 blocksoutany D.-C. component present. .When investigating D.-C. signals orD.-C. components of signals; the input is connected between terminals I6and 2?; 1 The incoming signal isthus direct connectedto the verticalamplifier ;without any blocking condenser, and hence, D. C.'-signalgvalues can be measured directly on the, screenpfthe oscilloscopeafter calibration by;v the known D,-C vo1tages from voltage divider 9.This is considered to be an improvement over the 'usual arrangementwhere a. blocking condenser is employed in the input circuit of thevertical amplifier,

The vertical andhorizontal amplifiers are supplied irom the --20 and+350 volt terminals of voltage divider 8. These amplifiers are similarand each comprises a pair of screen grid vacuum tubes 23 and Z4, 'an dthey are cathode connected phase inverters and p'roduce'output voltagesof opposite-polarity of a magnitude proportional to input. The output ofthe vertical amplifier is or may be impressed across the verticaldeflection plates 25 of the cathode-ray tube I through jumperconnections at 26, and the output of the horizontal or sweep amplifieris ormay be impressed across the horizontal deflection plates -21 of theoscilloscope through'jumpers at 28. The jumpers 26 and '21 are removablefor purposes to be explained later. The representationof the deflectionplatesisschematic. 1 Y

Positioning-control I provide a novel positioning control method for thevertical andhoi izontal amplifiersby inversely varying the'spreengridvoltages. In this controla voltage from a suitable intermediate sectionof voltagedivider 8 is impressed across four slide wire resistances Z9,30, 3l; and 32. Contacts 33 and 34 associated with the verticalandhorizontal amplifiers, respectively, which are adjustable along theseresistances connect with the screen grids of the respective tubes andsince the ous adjustment. The sllde wires zg and all are r 1 crossconnected to the voltage source such that as the voltage on the screengrid time or the tubes- 23 is increased, the screen gridvoltag of itscompanion tube 24 is reduced. Hence, moving contacts 33 in one directionwill movetheicath- J g ode-ray beam of the cathode-ray tube verticallyin one direction, and moving such contacts in the opposite directionwill move the beam in the opposite directioncnthe screen. The horizontalbea'in' control is similar except that, with it, the beam ma be shiftedhack and forth horizontally on the screen of thescope tube I. Thismethod ofjpositi'onirig' provides a continuously variable control andinstantaneous response for reference positioning of the' 'beam-i Itcompensates for differences in tube characteristics and the value ofplate load resistors ithus' making the pair-of tubes of each amplifieroperate as i nearly identical tubes} This method of positioning is notgreatly atfctedihy changes in line voltage so there is no needjfdr anelaborate-"regulated power supply. The plate currents flow through loadresistors such as indicated i at- 35-. In 'thevertical ampli fier,inductance, suchs showa atse, is also'preferably included'in the plate ccuits to improve the frequency response. filter network composedof-resistance anti-capacity isconnected across the plate leadimpedanceof tube-23. A connctionfl fis on this' network to provide avoltage for the v putposef of synchronizing .the swe; p 7 voltagegenerator with the input signal to the amplifier;

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' E;. he-1Q ?:Y I i fi e r: is a tendency io jgnagg rtned; Darwinianthecatho dist-ortedji hto an obal; of horizontal c s; caused bythe bythe parallel deadifi a in ential be ween the ea le -af 1 a ode-i i eeihv ti n re val deflectis n atesare; ssed e v deems alone i the; .od r fi'a the, e efl'ecw each air 9. 5;? atea erat aidiffrent e t oa u t. wecontro "Leave d s o e hatifthe i it the hs aaq e 3 5 f the athodean e; sr mm chassis ground, has n cot'r'espondifig to the average voltage ofthe horizontal and vertical defleeting plates,thissastigmatic;distortion, as it might be called, disappears and thebeam has a round shape giving" a sharp-even Widthtrace on the screen in;all directions ormove ent.

'Qn'e method or accomplishing-this end 'islshown in FigQl where anode3311s connected to the adjustablecontactbetween the plat'e'StiDmyvoltage for the vertical and horizontal amplifiers and ground; ,7Byadiustifig the antidistortion control 4, th'e second aneae voltageasean be niacle e'qual to the average voltage 6f the ren deflectingplates and theds'ire'd-rsult-ofa roundimage -on the cathode-ray tubescreen is obtained. The

the second anode 38 is also connected to all four deflecting platesthrough resistances 39 and 40, the resistances 39 being connected acrossthe vertical plates 25 With the connection to anode 38 at a midpointbetween the resistances. A similar connection is made from anode 38 tothe midpoint of resistances 40 connected between the horizontaldeflecting plates 21. Such a mesist ance between the deflecting platesand the anode '38 prevents the plates from accumulating electrostaticcharges; a

A second method of accomplishing correction for imageidistdrtionfisshown in Fig. 5 Where the second an6d;'; 8 :is connected to anintermediate voltage on' voltage divider 8. The high voltagesupply-rmains fordthe vertical and horizontal amplifirs are, inthisfigure, connected to the adjustable contact arms of slide wireresistors H and 18 respectively. The resistors 71 and 1B are nu cdebetweea m 1 29 Q iY 9. .t ol aeldi a th neinifiq w ighai d In yst ntieglate-su ply b ex; is adjusteduntil the 4. re e t d fleci li a esequals. hevo aee .r haew mane W this condition has; been at ained the;image on the screen; of thex cathode ray'tube; is round and Thislattersystem oi fers theadvantage over the previou i srstem q vv evid qan, ad u tm t of t se ond rase-there ale gi e acount a y; d treremes.twee he; v r ca s-and; e zontal amplifiers; Whereas, thei'lrstsystemproid l' nlran ad-Ma awi .ih.;fi. Q T practical results ot; thefirstsystem are; however; sufijciently good nd pp most applications thissystemwill be found be adeguata There are ot-coug'seother met s whichcan belised to make he "v taee i; h-S l dhi fi 38-Jeq11a1 to the ayeragevoltages; of the-deflecting plates fiandfll; i r i The sweep eegieraterI3 isof conventional desi'g'ri but; the eomi 'etiemo the horizontalamplifier rromthe'sw'e'ep voltage generator is believed to represent ani movement-in that it-is designed so as to minimizedistortiohbfthehwedvbltage. The selected eendriser of thesweep-generator is charge through an adjustable control resistor-4| andresistors- 42 ana- 43 frornacross the voltage divider resistance9,:Qa'r'iddischargedthroilgh the gaseou tube 4'4: s-ares'mt the voltageacross tube" 54 gradually builds up and 7 suddenly decreases to zero,producing thwell known triangular shape sweepvoltage Wave. A correspondng voltage- "is fed to .thefinputmof the horizontal amplifier foramplification fas desired. one ditliciilty heretofore has been infeeding this widely and sug'idenlywar'ying'v voltage to ith'ezcontro'lgridofa th e horizontal amplifier without distortione I em my 'afc'althodl 'follower tube 45 which performs a direct currenttransformervol ta'ge across the sweep generator; The input voltage to. the control;gi'idnr horizontal amplifier tube 23ii's taken \offt of an adjustable.point .of. 'the cathode; follower; resistance;46ithrough a slide wirecontact and connection 4.1.; This connection includes a further slidewire resistance 48 connected to groundwith an adjustable contact fromresistance 48.t'o.the control grid of horizontal amplifier tube 23; Itis'evident that the current which flows through resistances 46 and 48 isnot taken fromlthe sweepgenerator but is merely controled in proportionto the value of sweep generator voltage, and hence, there is minimumdistortion of the sweep voltage applied to the horizontal amplifier. v

There is a synchronizing selector switch associated with the horizontalamplifier and sweep generator control, and the connection just describedis made through the upper blade 49 of this switch in any one of fourpositions. In the extreme left-hand position of switch blade 49 thehorizontalamplifier maybe connected to an external source of voltagethrough a terminal 50. The terminal which is connected to be controlledby the sweep generator through a condenser 52 is used when it is desiredto synchronize the operation of some external device, such as anelectronic switch, with the oscilloscope operation. The lower blade 53of the selector switch is connected to the control grid circuit of sweepgenerator gaseous tube 44. When the horizontal amplifier input iscontrolled by an external source of sweep frequency with switch blade 49connected to terminal 50, the blade 53 which is connected to and moveswith blade 49 is connected to a ground terminal 54. In the next positionof the selector switch movin clockwise, the sweep generator inputcontrol is connected to a terminal 55 to enable the sweep generator tobe synchronized with the frequency of an external signal which will beconnected at terminal 55. In the next or third position of the selectorswitch, switch blade 53 connects the sweep generator control to a leadmarked A which connects to a point marked A just above rectifier tube 6,and which is connected to the cathode of this double wave rectifier.With a Bil-cycle power supply to transformer 5 the point A will have afrequency of I20 cycles per second and the sweep generator 13, whenproperly adjusted to near this frequency, will be synchronizedaccordingly. In the next or fourth position of switch 53 it is connectedto a lead marked X which connects with the filament supply found in thelower right-hand corner of Fig. 1 and which has a synchronizingfrequency of 60 cycles. In the final or fifth position of thesynchronizing blade 53 of the selector switch, the sweep generatorsynchronizing control is connected through wire 31 with the verticalamplifier circuit, so that the sweep generator l3 will be synchronizedwith the signal frequency applied at |5 -22 or s-22 to the verticalamplifier. The sweep generator is made to synchronize with the selectedfrequency by turning it to a condition where its natural frequency willbe near the selected control frequency by the capacitance control switch80, variable resistance 41 in the charging circuit of the sweepgenerator, and the input grid voltage control potentiometer at 56.

The oscilloscope with its control system power supply etc. is adapted tobe housed in an ordinary luggage case 57, Fig. 2, the cover 58 ofwhichis removable by opening in the usual way and then sliding it 01? ofits hinges 59. The luggage case with oscilloscope inserted and withcover removed is shown in Fig. 2, in which condition the apparatus isready for use. The scope tube I with its chassis is removable as a unitfrom the carrying case by removing six nuts 60 from bolts 6| whichextend through the front panel 62. A rear view of the chassis as removedfrom the carrying case is shown in Fig. 3. The bolts-flare secured inwooden cleats 63 fastened in the luggage case at the necessary-points.In one corner of the carrying case is a built-in compartment 64-for thestoring of the necessary connector cables, accessories, and a pair ofplug-in attenuators 55 and 66, the attenuator 66 being shown in itscompartment and the attenuator 65 removed in Fig. 2. The attenuators 65and Behave different resistance ranges and are used interchangeably whenthe signal voltage to be investigated is suificiently high as to makethe use of the vertical amplifier unnecessary. These attenuators havethree plugs extending from their back sides, identified as 61a, 68a, and6m (see-Fig. 4) positioned to fit into plug sockets between the verticalamplifier and vertical deflection plates and identified in Fig. 1 as 61,68 and BI, respectively. The jumpers 26 in the vertical amplifier scopedeflection plate circuits are exposed on the front panel as shown inFig. 2 and are removable and use plug sockets 68 and 61, and whenremoved, either of the attenuators 65 or 66 may be plugged in.

When one of these attenuators is used, the signal which is usuallyapplied at terminals 22 and I5 or [6, Fig. 1, is applied to a pairofterminals l0 and H on the attenuator. The connection of theseterminals to plug sockets Bla, 68a and 51a. and to the adjustablerh'eostat 12 of the attenuator is shown in Fig. 4, together with theplug socket connections BI, 61 and 68 on the panel.

In Fig. 2 the various terminals and controls are identified by referencecharacters used in Fig, 1 for the corresponding part. It is to be notedthat these are readily accessible on the front or the panel when thecarrying case cover 58 is removed. The 110-volt, -eycle power supply isplugged into a socket at 13 and just to the right of this socket is afuse 14 in such power supply circuit. The power supply may be turned offand on by a switch 15, and when on, "a pilot light 16 lights. Groundconnection may be made at H or 22.

In order to house the cathode-ray tube 1 in the carrying case and to beable to view its screen from the front of the exposed panel shown inFig. 2, the tube is disposed longitudinally near the top of the carryingcase behind the panel, with its screen end to the left, and a 45 degreeangle mirror 18 is used to reflect the screen end of the tube at rightangles through a window 19. Another function served by this method ofmounting the cathode-ray tube in its carrying case is improved shadingfrom incident light. It is, therefore, much easier to observe the apattern on the screen of the tube as well as being able to see transientphenomena which might otherwise be obliterated by the strong roomlights.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A combined amplifier and positioner for cathode-ray Oscilloscopes foramplifying deflection plate voltages and positioning the cathoderaybeam, comprising a pair of vacuum tubes having plate, cathode, controlgrid, and screen grid electrodes, means for impressing the signal to beamplified on the control grid of one of said tubes, means connectingsaid tubes as a cathode coupled phase inverter, and. means forsimultaneously and inversely varying the voltage between the screengrids of said tubes and their bcja'mplifled'onthe control grid of" oneof said 10 tubes; connections for connecting; saiclitubesiasa cathodeconnected phase inverter; connections for? impressing the a tube plate:voltages :betweema pairof-' deflection platesofthe oscilloscope; avoltage divider'serving; as a source of supply for saiditubes, a" pairof resistances connecte'd across an intermediate portion of saidvoltage" divider, connections to the screen :gridsnffsaid tubes adjustableualong said; resistances, and t means; for simultaneouslymoving; both :otisaidi; connections toiinvers'ely vary the; screen: gridvoltages ofsaid tubes.

HARRY: A. CHALBERGL REEEREN-GES: GIT-ED The following references areofrecord in: the file, of this patent:

UNITED STATES PATENTS Number Name Date 2,188,647 Bnsse Jan. 30; 19472248;581 NOrgaa-rd' July-8," 1941 2,286,894 Browne-et-a1i June 16} 19422,315,848 G'eohegan Apr. 6,- 1943 25344-3344 Dorsman-c Mar. 14; 1944 t li i

